PostgreSQL 's statistics collector is a subsystem that supports collection and reporting of information about server activity. Waiting for a logical replication remote server to change state. The pg_stat_ssl view will contain one row per backend or WAL sender process, showing statistics about SSL usage on this connection. Waiting to read or update dynamic shared memory allocation information. The pg_statio_all_sequences view will contain one row for each sequence in the current database, showing statistics about I/O on that specific sequence. Note, however, that the existence of a session and its general properties such as its sessions user and database are visible to all users. But processes can also await other events: Waits for input/output ( IO) occur when a process needs to read or write data. See, One row per SLRU, showing statistics of operations. Waiting for a write when creating a new WAL segment by copying an existing one. Waiting for parallel workers to finish computing. Resets all statistics counters for the current database to zero. The pg_stat_all_indexes view will contain one row for each index in the current database, showing statistics about accesses to that specific index. Amazon Aurora PostgreSQL wait events - Amazon Aurora Waiting to access the transaction status SLRU cache. The pg_stat_database_conflicts view will contain one row per database, showing database-wide statistics about query cancels occurring due to conflicts with recovery on standby servers. Per-Backend Statistics Functions, Copyright 1996-2023 The PostgreSQL Global Development Group. might need to increase it or scale up your DB instance class. I am not the DBA, but receive reports occasionally when an application is causing load on the system. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Since collection of statistics adds some overhead to query execution, the system can be configured to collect or not collect information. This view will only contain information on standby servers, since conflicts do not occur on master servers. Time when this process was started. However, current-query information collected by track_activities is always up-to-date. See. The LWLock that this article will introduce is a lightweight lock (Lightweight Lock) based on SpinLock. Waiting for a write when creating a new WAL segment by copying an existing one. Most such locks protect a particular data structure in shared memory. idle in transaction: The backend is in a transaction, but is not currently executing a query. Waiting to retrieve or store information about serializable transactions. The LWLock:BufferIO event occurs when Aurora PostgreSQL or RDS for PostgreSQL is waiting for other processes to Identifier of this backend's most recent query. Total amount of time spent writing WAL buffers to disk via XLogWrite request, in milliseconds (if track_wal_io_timing is enabled, otherwise zero). Returns a record of information about the backend with the specified process ID, or one record for each active backend in the system if NULL is specified. LWLock:BufferIO - Amazon Relational Database Service AWSDocumentationAmazon RDS and Aurora DocumentationUser Guide Relevant engine versionsContextCausesActions LWLock:BufferIO Waiting for a timeline history file received via streaming replication to reach durable storage. The pg_stat_user_indexes and pg_stat_sys_indexes views contain the same information, but filtered to only show user and system indexes respectively. IPC: The server process is waiting for some activity from another process in the server. Waiting for mapping data to reach durable storage during a logical rewrite. Waiting for SSL while attempting connection. Waiting to create or drop the tablespace. A process can wait for the data needed from a client ( Client) or another process ( IPC ). 'Re: [HACKERS] [PATCH] Refactoring of LWLock tranches' - MARC Waiting for a new WAL segment created by copying an existing one to reach durable storage. Waiting to access the sub-transaction SLRU cache. Waiting for parallel bitmap scan to become initialized. For details such as the functions' names, consult the definitions of the standard views. This is controlled by configuration parameters that are normally set in postgresql.conf. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. If, Type of current backend. The pg_stat_replication view will contain one row per WAL sender process, showing statistics about replication to that sender's connected standby server. The server process is waiting for some condition defined by an extension module. Waiting in WAL receiver to receive data from remote server. A transaction can also see its own statistics (as yet untransmitted to the collector) in the views pg_stat_xact_all_tables, pg_stat_xact_sys_tables, pg_stat_xact_user_tables, and pg_stat_xact_user_functions. Waiting to read or update shared multixact state. Waiting to read or update information about synchronous replicas. Waiting to allocate or free a replication slot. If the standby server has entirely caught up with the sending server and there is no more WAL activity, the most recently measured lag times will continue to be displayed for a short time and then show NULL. The server process is waiting for an I/O operation to complete. The access functions for per-database statistics take a database OID as an argument to identify which database to report on. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). Therefore it is not safe to assume that all files older than last_archived_wal have also been successfully archived. Waiting for background worker to start up. Users interested in obtaining more detailed information on PostgreSQL I/O behavior are advised to use the PostgreSQL statistics collector in combination with operating system utilities that allow insight into the kernel's handling of I/O. If the argument is NULL, resets statistics for all the replication slots. Waiting for a logical replication remote server to send data for initial table synchronization. Waiting for parallel query dynamic shared memory allocation lock. wait_event will identify the specific wait point. Timeout: The server process is waiting for a timeout to expire. If you've got a moment, please tell us how we can make the documentation better. These times represent the commit delay that was (or would have been) introduced by each synchronous commit level, if the remote server was configured as a synchronous standby. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. See, One row per connection (regular and replication), showing information about GSSAPI authentication and encryption used on this connection. The pg_stat_slru view will contain one row for each tracked SLRU cache, showing statistics about access to cached pages. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. This is the only column in this view that returns a value reflecting current state; all other columns return the accumulated values since the last reset. Waiting to read or write relation cache initialization file. Each shared buffer has an I/O lock that is associated with the LWLock:BufferIO wait event, each time a block (or The pg_stat_wal_receiver view will contain only one row, showing statistics about the WAL receiver from that receiver's connected server. block. buffer_io: Waiting for I/O on a data page. Waiting in main loop of logical replication launcher process. Waiting in main loop of background writer process. See, One row per database, showing database-wide statistics. Waiting to read or update the progress of one replication origin. Normally these parameters are set in postgresql.conf so that they apply to all server processes, but it is possible to turn them on or off in individual sessions using the SET command. When the number of actual disk reads is much smaller than the number of buffer hits, then the cache is satisfying most read requests without invoking a kernel call. Waiting for SLRU data to reach durable storage during a checkpoint or database shutdown. The pg_stat_wal_receiver view will contain only one row, showing statistics about the WAL receiver from that receiver's connected server. Waiting to fill a dynamic shared memory backing file with zeroes. Waiting in main loop of WAL sender process. Current overall state of this backend. Topics Relevant engine versions Context Causes Actions Relevant engine versions Each such lock protects a particular data structure in shared memory. Waiting for a write of logical rewrite mappings. The latter will be less if any dead or not-yet-committed rows are fetched using the index, or if any heap fetches are avoided by means of an index-only scan. your experience with the particular feature or requires further clarification, being read from storage. Waiting for a write while creating the data directory lock file. Waiting for the version file to be written while creating a database. This effect can mean that you have a small shared buffers setting. Waiting in main loop of syslogger process. Cumulative statistics are collected in shared memory. Waiting to read or truncate multixact information. Top-level transaction identifier of this backend, if any. A process acquires an LWLock in a shared mode to read from the buffer and an exclusive mode to write to the buffer. The total number of rows in each table, and information about vacuum and analyze actions for each table are also counted. The following wait events are a subset of the list in Amazon Aurora PostgreSQL wait events. Priority of this standby server for being chosen as the synchronous standby in a priority-based synchronous replication. pg_stat_get_backend_activity ( integer ) text. For client backends, this is the time the client connected to the server. See, One row for each table in the current database, showing statistics about accesses to that specific table. Per-Backend Statistics Functions, pg_stat_get_backend_idset () setof integer. Table28.19. idle in transaction (aborted): This state is similar to idle in transaction, except one of the statements in the transaction caused an error. Waiting to read or update the state of prepared transactions. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. The parameter track_wal_io_timing enables monitoring of WAL write times. See. Time at which these statistics were last reset. In particular, when the standby has caught up completely, pg_stat_replication shows the time taken to write, flush and replay the most recent reported WAL location rather than zero as some users might expect. Number of times in-progress transactions were streamed to the decoding output plugin while decoding changes from WAL for this slot. In all other states, it shows the identifier of last query that was executed. Waiting to synchronize workers during Parallel Hash Join plan execution. Waiting to read or update a process' fast-path lock information. Occasionally i noticed that in random interval of times the dbms become slow and get stuck on a few SELECT queries. Waiting in main loop of logical replication apply process. Normally these parameters are set in postgresql.conf so that they apply to all server processes, but it is possible to turn them on or off in individual sessions using the SET command. streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. Waiting for SSL while attempting connection. Resets statistics to zero for a single SLRU cache, or for all SLRUs in the cluster. The buffer_mapping LWLock wait event will be . Waiting for the relation map file to reach durable storage. Number of times transactions were spilled to disk while decoding changes from WAL for this slot. Process ID of the parallel group leader, if this process is a parallel query worker. Send time of last reply message received from standby server. Table28.26.pg_stat_database_conflicts View, Number of queries in this database that have been canceled due to dropped tablespaces, Number of queries in this database that have been canceled due to lock timeouts, Number of queries in this database that have been canceled due to old snapshots, Number of queries in this database that have been canceled due to pinned buffers, Number of queries in this database that have been canceled due to deadlocks. Each individual server process transmits new statistical counts to the collector just before going idle; so a query or transaction still in progress does not affect the displayed totals. Re: [HACKERS] Sequence Access Method WIP The pg_statio_ views are primarily useful to determine the effectiveness of the buffer cache. When the buffer manager receives a request, PostgreSQL uses the buffer_tag of the desired page. Process ID of a backend or WAL sender process, Version of SSL in use, or NULL if SSL is not in use on this connection, Name of SSL cipher in use, or NULL if SSL is not in use on this connection, Number of bits in the encryption algorithm used, or NULL if SSL is not used on this connection. (Conflicts occur only on standby servers; see, Number of temporary files created by queries in this database. Note that this includes the transactions that are streamed and/or spilled. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. 202302_Serendipity_Shy_CSDN In contrast, when starting from an unclean shutdown (e.g., after an immediate shutdown, a server crash, starting from a base backup, and point-in-time recovery), all statistics counters are reset. When analyzing statistics interactively, or with expensive queries, the time delta between accesses to individual statistics can lead to significant skew in the cached statistics. PostgreSQL Entangled in Locks: Attempts to free it - Amit Kapila - Dilip Kumar PGCon 2017 . PostgreSQL Source Code: src/include/storage/lwlock.h Source File proc: Waiting to read or update the fast-path lock information. Monitoring systems should choose whether to represent this as missing data, zero or continue to display the last known value. async: This standby server is asynchronous. Waiting to access the multixact member SLRU cache. Monitoring systems should choose whether to represent this as missing data, zero or continue to display the last known value. See, One row per connection (regular and replication), showing information about SSL used on this connection. Waiting for a write during reorder buffer management. For example, to show the PIDs and current queries of all backends: Table28.35. Indexes can be used by simple index scans, bitmap index scans, and the optimizer. Waiting to send bytes to a shared message queue. OID of the database this backend is connected to, Name of the database this backend is connected to. Waiting for startup process to send initial data for streaming replication. Waiting for other Parallel Hash participants to finish loading a hash table. Lag times work automatically for physical replication. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData. This can be used to gauge the delay that, Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. Type of current backend. 106 . Waiting to access predicate lock information used by serializable transactions. 28.2.3. Process ID of the subscription worker process, OID of the relation that the worker is synchronizing; null for the main apply worker, Last write-ahead log location received, the initial value of this field being 0, Process ID of a backend or WAL sender process, Version of SSL in use, or NULL if SSL is not in use on this connection, Name of SSL cipher in use, or NULL if SSL is not in use on this connection, Number of bits in the encryption algorithm used, or NULL if SSL is not used on this connection, True if SSL compression is in use, false if not, or NULL if SSL is not in use on this connection, Distinguished Name (DN) field from the client certificate used, or NULL if no client certificate was supplied or if SSL is not in use on this connection. Serial number of the client certificate, or NULL if no client certificate was supplied or if SSL is not in use on this connection. IP address of the client connected to this backend. Port number of the PostgreSQL instance this WAL receiver is connected to. The argument can be one of CommitTs, MultiXactMember, MultiXactOffset, Notify, Serial, Subtrans, or Xact to reset the counters for only that entry. Waiting to write a protocol message to a shared message queue. Waiting to access the commit timestamp SLRU cache. The Internals of PostgreSQL : Chapter 8 Buffer Manager - Hironobu SUZUKI If you see anything in the documentation that is not correct, does not match Waiting for a replication origin to become inactive to be dropped. TCP port number that the client is using for communication with this backend, or -1 if a Unix socket is used. Waiting to access a shared TID bitmap during a parallel bitmap index scan. Prevent sudden database connection spikes by using a connection pool. Waiting for SLRU data to reach durable storage following a page write. Waiting for truncate of mapping data during a logical rewrite. It also tracks the total number of rows in each table, and information about vacuum and analyze actions for each table. Client: The server process is waiting for some activity on a socket from user applications, and that the server expects something to happen that is independent from its internal processes. Lock: The backend is waiting for a heavyweight lock. Java_Java_File_Io_Buffer - See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. Waiting for a serialized historical catalog snapshot to reach durable storage. Waiting for data to reach durable storage while assigning WAL sync method. The parameter track_activities enables monitoring of the current command being executed by any server process. Waiting for a write to a replication slot control file. Returns the wait event type name if this backend is currently waiting, otherwise NULL. The parameter track_io_timing enables monitoring of block read and write times. The management of the buffers in PostgreSQL consists of a buffer descriptor that contains metadata about the buffer and the buffer content that is read from the disk. Here is an example of how wait events can be viewed: The pg_stat_replication view will contain one row per WAL sender process, showing statistics about replication to that sender's connected standby server. Similarly, information about the current queries of all sessions is collected when any such information is first requested within a transaction, and the same information will be displayed throughout the transaction. Ordinary users can only see all the information about their own sessions (sessions belonging to a role that they are a member of). This has no effect in a quorum-based synchronous replication. These times represent the commit delay that was (or would have been) introduced by each synchronous commit level, if the remote server was configured as a synchronous standby. Waiting to read or update vacuum-related information for a B-tree index. Waiting for the page number needed to continue a parallel B-tree scan to become available. Possible types are autovacuum launcher, autovacuum worker, logical replication launcher, logical replication worker, parallel worker, background writer, client backend, checkpointer, archiver, startup, walreceiver, walsender and walwriter. Verify whether you have unused indexes, then remove them. These numbers do not act as stated above; instead they update continuously throughout the transaction. Total amount of data written to temporary files by queries in this database. Waiting for a relation data file to be truncated. Waiting to associate a data block with a buffer in the buffer pool. 5mins of Postgres E25: Postgres lock monitoring, LWLocks and the log Connection string used by this WAL receiver, with security-sensitive fields obfuscated. Waiting to read or update the state of logical replication workers. The pg_statio_all_tables view will contain one row for each table in the current database (including TOAST tables), showing statistics about I/O on that specific table. For more information on lightweight locks, see Locking Overview. pg_stat_reset_subscription_stats ( oid ) void. Waiting to access the serializable transaction conflict SLRU cache. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). The pg_statio_all_sequences view will contain one row for each sequence in the current database, showing statistics about I/O on that specific sequence. Heavyweight locks, also known as lock manager locks or simply locks, primarily protect SQL-visible objects such as tables. The pg_stat_database view will contain one row for each database in the cluster, showing database-wide statistics. Waiting for WAL buffers to be written to disk. streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. pg_stat_reset_replication_slot ( text ) void. Waiting for WAL from a stream at recovery. query performance - PostgreSQL LWLock: lock_manager issue - Database Time spent reading data file blocks by backends in this database, in milliseconds (if track_io_timing is enabled, otherwise zero), Time spent writing data file blocks by backends in this database, in milliseconds (if track_io_timing is enabled, otherwise zero), Time spent by database sessions in this database, in milliseconds (note that statistics are only updated when the state of a session changes, so if sessions have been idle for a long time, this idle time won't be included), Time spent executing SQL statements in this database, in milliseconds (this corresponds to the states active and fastpath function call in pg_stat_activity), idle_in_transaction_time double precision, Time spent idling while in a transaction in this database, in milliseconds (this corresponds to the states idle in transaction and idle in transaction (aborted) in pg_stat_activity), Total number of sessions established to this database, Number of database sessions to this database that were terminated because connection to the client was lost, Number of database sessions to this database that were terminated by fatal errors, Number of database sessions to this database that were terminated by operator intervention. BufferPin: The server process is waiting to access to a data buffer during a period when no other process can be examining that buffer. The easiest way to create a cross-Region replica for Amazon RDS for PostgreSQL is by completing the following steps: On the Amazon RDS console, choose your Amazon RDS for PostgreSQL source instance. pg_stat_get_backend_client_port ( integer ) integer. Waiting to associate a data block with a buffer in the buffer pool. See Table28.4. Waiting to access a shared tuple store during parallel query. Waiting during recovery when WAL data is not available from any source (. Additional Statistics Functions. Waiting to ensure that the table it has selected for a vacuum still needs vacuuming. please use Waiting in background writer process, hibernating. See, At least one row per subscription, showing information about the subscription workers. pg_stat_get_backend_userid ( integer ) oid. 214 . pg_stat_get_activity ( integer ) setof record. If the state is active and wait_event is non-null, it means that a query is being executed, but is being blocked somewhere in the system. The pg_statio_ views are primarily useful to determine the effectiveness of the buffer cache. Waiting to elect a Parallel Hash participant to allocate more batches. Waiting in main loop of autovacuum launcher process. Waiting to read or update notification messages. Waiting for truncate of mapping data during a logical rewrite. LWLock- buffer_mapping. to keep index reordering low and reduces its impact. Wait Events of Type Extension. The statistics collector transmits the collected information to other PostgreSQL processes through temporary files. Another important point is that when a server process is asked to display any of these statistics, it first fetches the most recent report emitted by the collector process and then continues to use this snapshot for all statistical views and functions until the end of its current transaction. idle in transaction (aborted): This state is similar to idle in transaction, except one of the statements in the transaction caused an error. See, One row for each tracked function, showing statistics about executions of that function. Waiting for logical rewrite mappings to reach durable storage. Resets statistics for a single table or index in the current database or shared across all databases in the cluster to zero. Number of times WAL files were synced to disk via issue_xlog_fsync request (if fsync is on and wal_sync_method is either fdatasync, fsync or fsync_writethrough, otherwise zero).